Interlocking system for railroads



C. S. BUSHNELL INTERLOGKING SYSTEMFOR RAILROADS Filed Dec. 4, 1954 June 2, 1936.

- ATTORNEY rent flow. of the switch machine to its normal position Patented June 2, 1936 v V 'UNITED STATES PATENT OFFICE INTERLOCKING SYSTEM FOR. RAILROADS Charles S. Bushnell, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application December 4, 1934, Serial No. 755,923

7 Claims. (Cl. 2463) This invention relates to interlocking systems SML may be moved into a normal position N in for railroads and it more particularly pertains ,to which it is illustrated in the drawing or into a a system employing asymmetric units in certain reverse position R indicated by dotted. lines in relay circuits for controlling the direction of ourthe drawing. Lever SML controls the operation In one type of electric interlocking systems for through the medium of a switch machine conrailroads to which the present invention more trol relay WN and to its reverse position through particularly relates the switches, signals or other the medium of switch machine control relay WR. traflic controlling devices are operated from a The switch machine, through its point detecremote point such as a tower or the like. Simitor contacts PD, controls the operation of a larly, information regarding the positions and switch repeating relay WP. This relay when de- 10 conditions of the various trafiic governing devices energized repeats the unlocked condition of the is transmitted from the remote point where these switch machine, when energized with its polar devices are located, to the tower in the form of contact to the left repeats the condition of the indications for giving the operator this informaswitch machine in its normal locked position and tion in a readily discernible form. when energized with its polar contact to the In accordance with the present invention it is right repeats the condition of the switch maproposed to connect an indication relay in series chine in its reverse locked position. The conwith a normal and a reverse asymmetric unit by t of ay W s a effected y t p rati normal and reverse contacts of a switch machine of lever SML so that the track switch and the lever in the tower and to apply direct current Switch machine level must be in Corresponding of a normal and a reverse polarity from a source positions be e the relay can be energizedof current at the remote location in .a manner Since the Control y the WP relay in ts and for a purpose which will be explained in mal and reverse positions is immaterial to an undetail. derstanding of the present invention, the circuits An object of the present invention i t o controlled by this relay are omitted. It will be arrange the circuits that high potentials or surges obvious that pol Contact 50 y e used to due to induced currents in the circuit of the control a y desired i i n vi asymmetric devices or rectifiers are allowed to East bound trafiic over track switch TS is condissipate while the rectifiers are disconnected trolled by Signal ES and West bound fio ov r from the circuit, instead of allowing these potenthis track t h is Controlled y Signals WS and tials to be impressed across a rectifier with the but Since this portion of the Syst forms consequent tendency toward breaking down and no part of the present invention the details of short-circuiting the rectifier unit. such control have been omitted.

Various other objects, purposes and character- Since the voltage of t battery Which oristic features of the present invention will be giZoS Conductors and I6 is o d ri y rather in part obvious from the accompanying drawing high, potentiometer PN iS provided to ause a and in part pointed out as the description propotential drop so that a low resistance WP relay gresses. and low voltage rectifiers can be used.

One form of apparatus employing the present Operation.-With the circuits in the condition 40 invention will be described and the novel feaillustrated n e dToWing, e y N is enertures will be pointed out in the claims. gized over a circuit extending from con- The accompanying drawing is a diagrammatic tact ID of lever SML in its full line position, back view illustrating one form of apparatus embody- Contact ll of relay WR and Winding of relay W ing the present invention. to Relay WP is energized over a circuit ex- Apparatus.Reierring to the drawing, the reftending from point detector contact 12 in erence character TS designates a railway switch its full line position, conductor 13, winding of which is operated by a switch machine SM. This relay WP, contact M of lever SML in its full line machine may be, for example, of the type shown position, rectifier l5, potentiometer resistance [8, in the patent to W. K. Howe, No. 1,466,903, dated conductor I6 and point detector contact IT, to September 4, 1923. Current flows in the proper direction over The switch machine is controlled by a manuthis circuit to position the polar contact of relay ally operated switch lever SML which may, for WP to the left (normal) position, example, be one of a group of similar lovers in It will now be assumed that it is desired to an interlocking machine. As here shown, lever reverse switch TS. To accomplish this result,

lever SML is moved from its normal to its reverse position thereby deenergizing relay WN and closing a circuit for picking up relay WR which extends from (-1-), contact iii of. lever SML in its dotted line position, back contact I!) of relay WN and winding of relay WR, to The movement of contact id to its dotted line position deenergizes relay WP because rectifier 25 is connected in the wrong direction for current to flow over the circuit established at the point detector contacts.

With relays WN and WP deenergized and relay WR picked up, a circuit is closed for operating switch machine SM to its reverse position which extends from front contact 20 of relay WR, back contact ii of relay WN, back contact 22 of relay WP, conductor 23, switch machine SM, conductor back contact 26 of relay WP, back contact 2? of relay WN and front contact 28 of relay WR, to

As soon as the switch is in its reverse locked condition a circuit is closed for energizing relay WP which extends from point detector contact H in its left hand dotted position, conductor IE, potentiometer resistance l8, rectifier 25, contact hi of lever SML in its dotted line position, winding of relay WP, conductor l3 and point detector contact H2 in its left hand dotted position, to Current flowing in this circuit picks up the neutral contacts of relay WP and positions its polar contact to the right.

If it is desired to restore switch TS to its normal position, lever SML is restored to its full line position as shown in the drawing. When contact In of lever SML is shifted from its dotted line to its full line position relay WR is deenergized and relay WN is energized. When contact id of lever SML is shifted from its dotted line to its full line position relay WP is deenergized. A circuit is now effective to operate the switch machine to its normal position extending from back contact 26 of relay WR, front contact 27 of relay WN, back contact 26 of relay WP, conductor 26, switch machine SM, conductor back contact 22 of relay WP, front contact 2i of relay WN and back contact 23 of relay WR, to When the point detector contacts reach their normal positions the previously described circuit is closed for energizing relay WP through contact i i of lever SML in its normal position. This picks up the neutral contacts of relay WP and positions its polar contact to the left.

It will be apparent from the foregoing that relay WP remains energized when a change is not taking place in the system. Current is therefore flowing through one rectifier or the other in series with relay WP depending upon the position of lever SML and the point detector contacts. With relay WP normally energized a potential is established across the terminals of the winding of this relay and when the circuit including the relay winding is deenergized a high momentary surge takes place which may reach considerable magnitude.

It has been found in using rectifiers in circuits of this type that the high momentary potentials developed in the circuit may be sufiicient to injure or break down the rectifiers if precautions are not taken. For example, in a circuit with the rectifiers short-circuited by the lever contacts when in closed positions, the movement of the lever leaves the rectifiers in circuit so that the high surge of current in the circuit due to the sudden interruption of the current flow from the battery is quite likely to injure them. Of course surge suppressors in the form of resistors or capacitors may be provided to by-pass these high potentials but the present invention accomplishes the desired result without the aid of such devices.

For example, with the circuits in the condition shown in the drawing there is a potential on the right hand terminal of the WP relay Winding and a potential on the left hand terminal of this winding. When contact I4 is suddenly broken the self inductance of the circuit tends to keep current flowing by setting up an induced potential to cause a current to flow in the same direction. This induced potential is proportional to the rate of change of the current and since the current has a tendency to die out very rapidly when the circuit is broken, the induced potential may be very great and cause a heavy momentary surge of current in the circuit. Since the only path for current to flow after contact i4 is open is through the air, arcing takes place at the contact and the current due to the induced high potential flows through the circuit in the same direction. This allows the surge to be dissipated through rectifier 55 before contact E4 is made in its reverse position.

It will be understood that this momentary heavy surge of current takes place during the interval between the breaking of contact M in its normal position and the making of contact M in its reverse position. If this momentary heavy surge were not dissipated before contact l4 reaches its reverse position then it would have a tendency to break down rectifier 25 because this rectifier is connected in the circuit in the wrong direction for the current to flow through the remainder of the circuit.

The same discussion applies to the inductive kick from relay WP when lever SML is moved from its reverse to its normal position except that this momentary surge then flows through rectifier 25 and through the are at contact 14 just leaving its reverse position. This is because the point detector contacts will be in their reverse positions for applying a potential to the left hand terminal of the WP relay winding and a potential to the right hand terminal of this winding.

Although I have herein shown and described only one form of railway track controlling apparatus embodying my invention it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit or scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, a contactor controlled by the track switch, an indication relay, a pair of asymmetric units, energizing circuits for the indication relay including the lever, the contactor, and the units and completed only when the lever and the contactor occupy corresponding positions, the lever being arranged to include only one said unit in circuit with the lever and the contactor at any one time.

2. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, a contactor controlled by the track switch, an indication relay, a pair of asymmetric units, energizing circuits for the indication relay including the lever, the contactor, and the units and completed only when the lever and the contactor occupy corresponding positions, the lever being arranged to include one or the other of said units, but not both, in series with the lever and the contactor.

3. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, a contactor controlled by the track switch, an indication relay, a pair of asymmetric units, energizing circuits for the indication relay including the lever, the contactor, and the units and. completed only when the lever and the contactor occupy corresponding positions, the lever being arranged to include one or the other of said units, but not both, in series with the lever and the contactor, and means controlled by said relay for preventing the actuation of said switch.

4. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, an indication relay, a contactor controlled by the switch, a circuit including said relay and connecting said lever and said contactor, a first and a second asymmetric unit, means controlled by said contactor for applying positive or negative current to said circuit, means controlled by said lever for selectively connecting said asymmetric units in said circuit, means responsive to the application of positive current to said circuit for energizing said relay in one direction in series with said first asymmetric unit, means responsive to the application of negative current to said circuit for energizing said relay in another direction in series with said second asymmetric unit, and means for dissipating the self induced current in said circuit as said first asymmetric unit is removed from the circuit and before the second asymmetric unit is included in any circuit.

5. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, an indication relay, a contactor controlled by the switch, a circuit including said relay and connecting said lever and said contactor, a first and a second asymmetric unit, means controlled by said contactor for applying positive or negative current to said circuit, means controlled by said lever for selectively connecting said asymmetric units in said circuit, means responsive to the application of positive or negative current to said circuit for energizing said relay in series with the first or second asymmetric unit as selected by said lever, and means responsive to the operation of said lever for deenergizing said circuit and for introducing a time delay before again energizing said circuit through the other unit whereby the self induced current in said circuit is dissipated before the succeeding asymmetric unit is connected in said circuit.

6. In combination, a railway track switch, a manually operable lever having normal and reverse positions, means responsive to the operation of said lever to its normal and reverse positions for actuating said switch to corresponding positions, an indication relay, a contactor controlled by the switch, a circuit including said relay and connecting said lever and said contactor, a first and a second asymmetric unit, means controlled by said contactor for applying positive or negative current to said circuit, means controlled by said lever for selectively connecting said asymmetric units in said circuit, means responsive to the application of positive or negative current to said circuit for energizing said relay in series with the first or second asymmetric unit as selected by said lever, means responsive to the operation of said lever for opening said circuit including one only of said units and for introducing a time delay before again closing said circuit including the other, only, of said units, whereby the self induced current in said circuit at the time of opening the same is dissipated before the other asymmetric unit is connected in said circuit, and a potentiometer connected to said circuit for reducing the potential applied to the selected asymmetric unit.

'7. In combination, a railway track switch having normal and reverse positions, a manually operable lever having normal and reverse contacts, a relay, means including a first asymmetric unit for supplying said relay with current of one polarity when and only when the normal contacts of said lever are closed and said switch occupies its normal position, means including a second asymmetric unit for supplying said relay with current of the opposite polarity when and only when the reverse contacts of said lever are closed and said switch occupies its reverse position, and means controlled by said lever contacts for momentarily interrupting every circuit including said relay and an asymmetric unit.

CHARLES S. BUSHNELL. 

